The aim of these studies was to establish the importance of temperamental properties and defensive coping styles described as Type C as well as anti-emotionality towards the etiology of breast cancer. The Pavlovian Temperament Survey was used in order to measure the temperamental properties. Type C was measured using the Polish version of Scale 1 for Type C evaluation from the Grossarth-Maticek and Eysenck Personality-Stress Questionnaire. Anti-emotionality was measured by the Polish versions of Marlowe­Crowne's Social Desirability Scale and Taylor's Manifest Anxiety Scale. The studies were of semi-prospective nature. The women with undiagnosed breast cancer were examined and then subdivided according to the medical diagnosis into the experimental group (women suffering from cancer; N=63), and the control group (women suffering from milder diseases; N=160). The additional group was composed of healthy women (N = 100). 323 women were examined overall. The analysis of the results demonstrated that Type C, of seemingly low anxiety and the temperamental variable – the strength of inhibition, plays an essential role in the etiology of cancer.